Methane is a significant greenhouse gas. One ton of methane is equivalent to approximately 21 to 22 tons of carbon dioxide with respect to its global warming potential. As a result, the reduction of one ton of methane emissions can be considered as achieving a reduction of 21 or more tons of carbon dioxide and can generate about 21 tons of carbon credits (as carbon dioxide) in the evolving Greenhouse Gas (GHG) market. Moreover, methane has about a 12 year half life in the atmosphere and is increasing worldwide at an annual rate of around one half of one percent (0.5%) per year. Accordingly, reduction of presently excessive methane emissions into the atmosphere is most desirable.
The emission of greenhouse gases (GHG) including methane from bovines and other ruminants is believed to be a significant contributor to global warming. Some scientists estimate that livestock contributes up to thirty-seven percent (37%) of the total global methane (CH4) budget. Methane emission from bovine sources, of which the majority is through belching, can be significantly reduced through modification of cattle diet. Attempts at reduction typically involve using nutrient blocks or other feed supplements while other efforts have concentrated on modification of the genetic composition of the animal herd. To date, efforts to measure and potentially remediate this source of GHG from ruminants have not been considered feasible or widely implemented in part because of high costs related to monitoring CH4 emission from ruminants in coordination or concurrently with measurement of supplement use.
Ruminants produce significant amounts of methane during their digestive processes. The multi-stage digestion system in ruminants contains substantial microbial consortia, which through anaerobic digestion breaks down food components to create low molecular weight fatty acids, alcohols, and microbial protein that travel through the gut and become reabsorbed. Methane emissions are a consequence of this process and constitute an energetic loss equivalent of from a third of a pound to potentially one half a pound of potential weight gain per head of beef cattle per day. Energetic losses from particular ruminants such as dairy cows are likely even higher than these estimates. Carbon dioxide and methane produced in the rumen is eructated or belched through the animal's nostrils and mouth. On average an animal belches about every 40 seconds. In addition to methane release causing GHG concerns, the production of methane by ruminants and its loss through eructation represents a significant energy loss to ruminant animal production efficiency. As diet quality decreases, methane emissions as a fraction of gross energy intake rises and dietary efficiency decreases. Therefore, the ability to monitor changes in the production of methane from ruminants provides a tool to monitor and diagnose digestion efficiency as well as to monitor levels of GHG emissions. Some recent studies have indicated that methane production is a function of animal genetics, animal diet and other factors that affect rumen microbial flora. The ability to easily monitor changes in methane production under field conditions represents a significant improvement in animal management capabilities.
The loss of methane is a significant energy loss to the animal. Globally this is equivalent to trillions of dollars of lost dietary efficiency. Animal nutritionists know that the metabolic pathways in the rumen can be modified by diet to reduce methane production and to more efficiently process feed. Several dietary supplements are available, and, in many cases, the cost of the nutrient supplement is easily exceeded by the animal weight gains, making use of supplements attractive to ruminant producers such as the cattle industry. Accordingly, reduction in methane emissions by ruminants can help animals become more productive per unit of forage or feed while also reducing undesirable methane emissions. When animals eat low quality forage, it actually takes a longer time to pass through their gut. Hence, the poorer the quality of forage, the longer it takes the animals to digest the forage, and this results in lower weight gain but more methane production. However, since monitoring of changes in methane performance under actual field conditions has been difficult or impossible to achieve in the past, it is not practical to modify forage composition to minimize methane losses nor to monitor and modify genetic factors that influence ruminant methane production. A system that can monitor changes in relative methane emissions could therefore provide important information to ruminant producers concerning optimal forage and grazing conditions. In addition, since animals fed a highly energetic diet process that feed more quickly, they produce more methane per unit time, but much less methane per unit of production of meat or milk. Therefore it can also be important to measure methane and carbon dioxide from the rumen as well as carbon dioxide from the animal's breath in order to differentiate rumen processes from catabolic and respiratory processes and to measure their emissions relative to measurements of animal production—such as animal weight gain and/or animal milk production.
U.S. Pat. No. 5,265,618 discloses a system that measures the flux of metabolic gas emissions from cattle or other animals. The system does not require that the animals be confined to a chamber or stall. An animal whose metabolic gas emissions are to be measured is first fed a permeation tube (i.e., a metal tube with a gas-permeable plastic disk in one end). Inside the tube is a tracer that is physiologically inert. The permeation tube is filled with pressurized liquid tracer, which slowly permeates in gaseous form through the plastic disk. In order to measure rumen-produced and respiratory metabolic gases, a sample container, such as an evacuated container or an inflatable collar, is placed on the animal. A small diameter sample tube is attached from the sample container to a halter and terminates somewhere near the animal's mouth. When the animal breathes, it exhales metabolic gases as well as the tracer. A sample of air containing both the metabolic gases and the tracer gas is then collected through the sample tube. Since the permeation rate of the tracer is known and constant, the ratio of the flux of a given metabolic gas to the flux of the tracer gas is equal to the ratio of the mixing ratios of the respective gases in the air sample that is collected. The rate of flux of metabolic gas from the animal's rumen is thus readily calculated by measuring the metabolic gas and tracer mixing ratios in the sample thus collected. This system, however, requires substantial animal handling and training to be effective. Moreover, it is not practical for animals that do not tolerate a halter, which may include large percentages of a ruminant herd. Also the system can only provide time-integrated values that represent average rumen, catabolic and respiratory processes. The system can not be used to track short-term changes nor can it isolate rumen processes from respiratory processes related to catabolism.
Schemes to convert increased ruminant metabolic efficiency into marketable GHG offsets have not been financially viable. Though mineral blocks, other effective nutrient supplements, and rumen-modifying antibiotics and ionophores are effective in reducing methane production and in many cases cost only a few cents per day, at the current value of greenhouse gas (GHG) offsets, compliance, documentation, and monitoring costs exceed the value of the GHG offsets that can be generated. Also, animals fed poor-quality forage have lower methane emission rates per unit time than animals fed high quality diets. However the emission of methane as a function of gross energy intake is much higher for an animal fed low quality forage compared to an animal fed a high quality diet. As a result methane per unit of animal production is much higher for low-quality, poorly digested forages compared to animals fed a high quality digestible diet. Specific nutrients, missing from low quality forage can be supplemented through the use of nutrient feeders to boost digestibility, resulting in increased efficiency and lower methane emissions per unit of animal production. It is therefore desirable to document relative changes in methane emission rates and it is not always necessary to measure fluxes of methane per unit of time. That is changes in ratios of methane compared to carbon dioxide for respiration as well as for rumen gas per unit of production can provide the information required to document animal performance improvements that lead to quantifiable methane reductions and can generate carbon credits. In addition, measurement of emissions of methane and carbon dioxide from the rumen and differentiation of this flux from measurements of carbon dioxide resulting from catabolism over shorter time periods are necessary in order to track energy flows through a specific ruminant and to document the efficiency of production of meat and milk in a way that facilitates interactive treatment to improve productive efficiency and lower methane emissions per unit of production.